Commit-ID: 973aa8181e10050809b56ecbaadd01495766a19e
Gitweb: http://git.kernel.org/tip/973aa8181e10050809b56ecbaadd01495766a19e
Author: Andy Lutomirski <luto@xxxxxxx>
AuthorDate: Mon, 23 May 2011 09:31:31 -0400
Committer: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitDate: Tue, 24 May 2011 14:51:29 +0200
x86-64: Optimize vDSO time()
This function just reads a 64-bit variable that's updated
atomically, so we don't need any locks.
Signed-off-by: Andy Lutomirski <luto@xxxxxxx>
Cc: Andi Kleen <andi@xxxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
Cc: Eric Dumazet <eric.dumazet@xxxxxxxxx>
Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Link: http://lkml.kernel.org/r/%3C40e2700f8cda4d511e5910be1e633025d28b36c2.1306156808.git.luto%40mit.edu%3E
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
---
arch/x86/vdso/vclock_gettime.c | 8 ++------
1 files changed, 2 insertions(+), 6 deletions(-)
diff --git a/arch/x86/vdso/vclock_gettime.c b/arch/x86/vdso/vclock_gettime.c
index e6e9f90..a69929e 100644
--- a/arch/x86/vdso/vclock_gettime.c
+++ b/arch/x86/vdso/vclock_gettime.c
@@ -180,12 +180,8 @@ notrace time_t __vdso_time(time_t *t)
if (unlikely(!VVAR(vsyscall_gtod_data).sysctl_enabled))
return time_syscall(t);
- do {
- seq = read_seqbegin(&VVAR(vsyscall_gtod_data).lock);
-
- result = VVAR(vsyscall_gtod_data).wall_time_sec;
-
- } while (read_seqretry(&VVAR(vsyscall_gtod_data).lock, seq));
+ /* This is atomic on x86_64 so we don't need any locks. */
+ result = ACCESS_ONCE(VVAR(vsyscall_gtod_data).wall_time_sec);
if (t)
*t = result;
--
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